Merged PR 1505517: Fix the stretch mode in PointEnterEffects

The stretch modes of EffectSource and ImageSource are different, make some images get clipped.

Related work items: #16159813

SampleGallery/Samples/SDK 10586/PointerEnterEffects/PointerEnterEffects.xaml.cs

@@ -153,6 +153,8 @@ namespace CompositionSampleGallery
             // Set the effect surface as input
             if (effectSurface != null)
             {
+                // Set to UniformToFill to match the stretch mode of the original image
+                effectSurface.Brush.Stretch = CompositionStretch.UniformToFill;
                 brush.SetSourceParameter("EffectSource", effectSurface.Brush);
             }
         }